The long term objective of the studies proposed in this application is to elucidate the mechanism(s) by which diabetes injures vessels and causes clinically significant vascular disease. A growing body of evidence indicates that: 1) many of the late complications of diabetes are linked to increased metabolism of glucose to sorbitol by the enzyme aldose reductase, and 2) aldose reductase-linked, diabetes-induced vascular damage and sorbitol metabolism are hormonally modulated. The experimental protocols are designed to achieve the following specific aims: 1) to elucidate the role of insulin deficiency independent of hyperglycemia, and vice versa, in the pathogenesis of diabetic vascular disease, 2) to clarify the roles of decreased tissue levels of myo-inositol and Na/K-ATPase activity in mediating diabetes-induced increases in vascular permeability, 3) to assess potential mechanisms by which sex steroids and thyroid hormone may modulate diabetes-induced alterations in polyol metabolism and vascular functional integrity, 4) to identify the mechanism(s) responsible for increased aldo- keto reductase activity in erythrocytes of diabetic rats, 5) to determine whether aldo-keto reductase activity in erythrocytes correlates with aldo-keto reductase activity and/or vascular permeability changes in sciatic nerve, aorta, and eyes in diabetic rats, 6) to investigate the relationship between aldo-keto reductase activity in erythrocytes, puberty, and glycemic control in human diabetics. The studies in rats will make extensive use of new methods and procedures developed in our laboratory which make it possible to assess direct effects of hormones, pharmacologic agents, and metabolic substrates on tissue metabolism and vascular permeability in vivo. Direct effects of hormones and metabolic substrates on these parameters are assessed on new granulation tissue formed in skin chambers in which test substances are applied topically to the tissue. Vascular permeability is assessed by permeation of 125I-albumin. Aldo-keto reductase activity (as opposed to ambient polyol levels) of red cells and tissues is assessed by measurement of galactitol accumulation during incubation with galactose in vitro. Tissue polyols are quantified as their butaneboronate derivatives using electron ionization gas chromatography/mass spectrometry. Na/K-ATPase activity is assessed by use of isotopic method. The information to be gained from these experiments should provide important new insights into the pathogenesis of diabetic vascular disease.